1. Field of the Invention
The present invention relates generally to cooling systems and techniques using vortex tubes.
2. Background Art
The use of vortex tubes (also know as the “Ranque Tube”, “Hilsch Tube”, “Ranque-Hilsch Tube”, and “Maxwell's Demon”) to implement systems for emitting colder and hotter gas streams is well known (See U.S. Pat. Nos. 1,952,281, 3,208,229, 4,339,926). A vortex tube offers a simple method of cooling using compressed air. Compressed air at high pressure is passed through a nozzle that sets the air in a vortex motion inside the vortex tube. A valve at one end of the tube allows the warmed air from this first vortex to escape. Some of the air that does not escape heads back up the tube as a second vortex inside the low pressure inner area of the larger first vortex. The inner vortex loses heat and exits through the other end of the tube as a cold air stream. Further description of vortex tubes can be found on the World Wide Web (See http://www.exair.com/vortextube/vt_page.htm). Thus the vortex tube takes compressed air as an input and outputs two streams of air, one heated and the other cooled.
In hydrocarbon exploration operations, there is a need to use electronic devices at temperatures much higher than their rated operational temperature range. With oil wells being drilled deeper, the operating temperatures for these devices keeps increasing. Besides self-generated heat, conventional electronics used in the computer and communications industry generally do not have a need to operate devices at high temperatures. For this reason, most commercial electronic devices are rated only up to 85° C. (commercial rating).
Modern tools or instruments designed for subsurface logging operations are highly sophisticated and use electronics extensively. In order to use devices that are commercially rated in a subsurface or downhole environment, it is highly desirable to have a cooling system capable of maintaining the electronics within their operational range while disposed downhole. Conventional logging techniques include instruments for “wireline” logging, logging-while-drilling (LWD) or measurement-while-drilling (MWD), logging-while-tripping (LWT), coiled tubing, and reservoir monitoring applications. These logging techniques are well known in the art.
Several approaches to extending the life of electronics in hot environments have been proposed in the past. U.S. Pat. No. 4,400,858 describes retainer clips that serve as heat sinks to conduct heat from the electronics to the tool housing to minimize temperature rise in the devices. U.S. Pat. No. 4,722,026 describes a method for reducing the temperature rise of critical devices by placing them in a dewar. U.S. Pat. No. 4,513,352 describes a dewar combined with heat conducting pipes to reduce the heating of electronics in a geothermal borehole. U.S. Pat. No. 4,375,157 describes a downhole refrigerator to protect electronics in the drilling environment. U.S. Pat. No. 5,720,342 proposes the use of a thermoelectric cooler attached directly to a multi chip module to cool the module. U.S. Pat. No. 5,730,217 describes a thermoelectric cooler used to cool electronics disposed in a vacuum to reduce heat gain from the ambient environment. Other methods to cool electronics using thermoelectric coolers are proposed in U.S. Pat. Nos. 5,931,000, 5,547,028 and 6,424,533. U.S. Pat. No. 6,341,498 proposes a cooling system including a container for a liquid and a sorbent to transfer heat from the electronics to the wellbore. U.S. Pat. No. 6,401,463 describes a cooling and heating system using a vortex tube to cool an equipment enclosure.
Vortex tubes have also been implemented in downhole instruments for cooling purposes. U.S. Pat. No. 2,861,780 describes a system using vortex tubes to cool the cutters of drill bits. U.S. Pat. No. 4,287,957 describes another system using a vortex tube to cool tool components. A drawback of the system proposed in the '957 patent is the need for a pressurized gas source at the surface for continuous gas feed, making the system impractical for many subsurface operations.
There remains a need for improved cooling techniques to maintain components at a temperature below the ambient temperatures experienced in hot environments, particularly electronics housed in instruments adapted for subsurface disposal, where rapid temperature variations are encountered.